1. Field of the Invention
The present invention relates to a catalytic combustion apparatus for gas turbine or an exhaust gas purifier apparatus having a honeycomb structure impregnated with a catalyst, and more particularly, to an apparatus for mounting the honeycomb structure in a tube of the combustion or purifier apparatus through which a high-speed high-temperature fluid flows.
2. Description of the Related Art
In a catalytic combustion apparatus for gas turbine, a honeycomb structure impregnated with a catalyst is mounted in a tube through which a high-speed high-temperature fluid, e.g., a combustion gas, flows downstream. In this arrangement, the combustion gas is subjected to a catalytic reaction, and its temperature is kept below a predetermined level (1,300.degree. C.), so that production of NO.sub.x is restrained. For the same purpose, an exhaust gas purifier apparatus is also provided with a honeycomb structure.
The honeycomb structure has upper- and lower-course end faces extending at right angles to the axial direction in which the combustion gas flows. The structure also includes a number of cells which allow the combustion gas to flow from the upper-course end face to the lower-course end face, and cause the gas to come into satisfactory contact with the catalyst. The honeycomb structure is formed of a ceramic material, e.g., cordierite, in order to be able to be fully impregnated with the catalyst. This ceramic material, however, is very brittle.
The honeycomb structure is surrounded and radially supported by a cylindrical supporting member which has a shock absorbing effect. Thus, even though the honeycomb structure and the tube are expanded to different degrees by the combustion gas, due to the difference in coefficient of linear expansion between them, the shock absorbing supporting member absorbs the force from the tube to press the structure. In this manner, the brittle honeycomb structure is prevented from being damaged.
The honeycomb structure is also supported in the axial direction of the tube. Thus, it is prevented from being dislocated in the axial direction by means of the high pressure of the combustion gas. More specifically, a ring-shaped fringe region of the lower-course end face of the honeycomb structure abuts against the ring-shaped supporting member. In this arrangement, the honeycomb structure is supported in the axial direction, and the combustion gas is allowed to flow out downstream from a central region of the lower-course end face of the structure.
The ring-shaped fringe region, however, is covered by the ring-shaped supporting member. Accordingly, the combustion gas cannot flow out downstream from the fringe region, and catalytic reaction can hardly take place in the fringe region. As a result, the temperature of the fringe region is lower than that of the central region. In other words, a temperature gradient is created in the radial direction of the honeycomb structure. Thus, tensile thermal stress may possibly be produced between the fringe region and the central region, and damage the structure.
In the exhaust gas purifier apparatus, a flow tube for an exhaust gas has a taper portion whose diameter becomes smaller with distance from its upper-course end. The lower-course edge of the honeycomb structure abuts against the taper portion, thereby axially supporting the structure. In other words, the lower-course edge of the honeycomb structure is supported by the tape portion in linear contact therewith. Therefore, catalytic reaction can take place even in the fringe region, and no thermal stress can be produced. The pressure of the exhaust gas in the purifier apparatus is lower than that of the combustion gas in the catalytic combustion apparatus. Thus, in the exhaust gas purifier apparatus, the honeycomb structure cannot be dislocated downstream even though it is supported by the taper portion only in linear contact therewith.
If the supporting method using the taper portion is applied to the catalytic combustion apparatus, however, stress may possibly be concentrated on the lower-course edge of the honeycomb structure, thereby damaging the structure, since the pressure of the combustion gas is relatively high.